1. Field of the Invention
This invention relates to fifth wheels in tractor-trailer vehicles and more particularly, to a cap, cover or insert for fitting over and tack-welding to the fifth wheel and an ultra high molecular weight (UHMW) polyethylene ingredient and elasticity modifying component combined to define a laminate composite and a method of constructing the composite. The laminate composite is applied to the bearing surface of a fifth wheel, trailer coupling plate or to the insert attached to the fifth wheel for reducing friction in the tractor-trailer coupling. In a preferred embodiment the insert is fitted with downwardly-extending tabs for tack-welding to the fifth wheel and the laminate composite is constructed of a mixture of ultra-high molecular weight polyethylene and a modulus of elasticity modifier such as carbon fibers to define a sheet material which is bonded to the fifth wheel or the fifth wheel insert to receive the trailer coupling plate. The laminate composite is characterized by superior toughness, wear-resistance, cold-flowing properties, modulus of elasticity and lubricity and is constructed by mixing ultra-high molecular weight polyethylene powder and an elasticity modifying component such as carbon fibers, applying heat and pressure to the mixture and producing the composite sheet.
Semi-trailers are traditionally and conventionally coupled to truck tractors by a coupling device which is known as a "fifth wheel". The fifth wheel includes a substantially round, flat, slotted plate positioned in a substantially horizontal plane on the truck tractor to define a bearing surface for attaching a corresponding coupling plate mounted on the trailer. The semi-trailer also includes a kingpin extending downwardly to locate and seat within the slot in the fifth wheel of the tractor. Once coupled, the trailer is allowed to pivot with respect to the tractor about the kingpin, with the trailer mounting surface or coupling plate bearing on the fifth wheel to permit the tractor and trailer to articulate when the tractor is turning. Grease applied to the fifth wheel normally serves to minimize friction and heat in the fifth wheel, but the grease cannot eliminate damage due to point and line stresses resulting from friction and rapid heat build-up when the trailer coupling plate momentarily bears on the fifth wheel in a non-uniform manner, a phenomenon which melts the grease, allows metal-to-metal contact under severe pressure and frequently causes damage to the fifth wheel and trailer coupling plate. Accordingly, it is difficult to maintain a uniform layer of grease between the two bearing surfaces joining the trailer and the tractor. Consequently, the grease must be frequently replaced, as it also tends to attract dirt and dust while the vehicle is on the road. Furthermore, as the grease is slowly eliminated from the trailer-tractor coupling due to friction and heat resulting from coupling articulation, the handling and performance characteristics of the rig tend to deteriorate and dangerous over-steering is a potential problem.
2. Description of the Prior Art
Various fifth wheel designs and techniques have been used to improve the bearing performance in the fifth-wheel trailer-tractor coupling. U.S. Pat. No. 5,066,035, dated Nov. 19, 1991, to Athans, et al, details a "Trailer Bearing Plate For Fifth Wheel". The device includes an assembly for coupling a tractor to a trailer, which assembly includes a fifth wheel bearing plate and a trailer bearing plate combination. A trailer bearing plate assembly includes a ring having a collar and is adapted to securely attach to an underside of the trailer. The trailer bearing plate further includes a disc disposed between the collar and the underside of the trailer. U.S. Pat. No. 3,174,812, dated Mar. 23, 1965, to M. Widmer, details a "Fifth Wheel Construction" for coupling an over-the-road truck tractor to a semi-trailer. The trailer plate assembly includes a ring having a collar adapted to securely attach to a trailer bearing plate housing. The housing is then secured to the underside of a trailer and the trailer bearing plate assembly further includes a disc disposed between the collar and the inner surface of the trailer plate housing. U.S. Pat. No. 4,169,635, dated Oct. 2, 1979, to Szalay, et al, details a fifth wheel bearing plate cover composed of a flat, sheet plastic material having a low coefficient of friction and high deflection characteristics, to provide a wear-resistant, slippery surface for contact with another bearing surface. A "Tractor Fifth Wheel Bearing Attachment" is detailed in U.S. Pat. No. 4,542,912, dated Sep. 24, 1985, to Andre'. The attachment includes an antifriction polyolefin plastic sheet mounted on the fifth wheel of a trailer.
It is an object of this invention to provide a new and improved fifth wheel cap, cover or insert for mounting on a fifth wheel and a laminate composite for attaching to a fifth wheel or to the fifth wheel cap, cover or insert, which composite includes high molecular weight polyethylene and a modulus of elasticity modifier and is designed to drastically reduce friction in the tractor-trailer coupling mechanism.
Another object of the invention is to provide a new and improved fifth wheel insert having tabs for tack-welding the insert in position on the fifth wheel and a high molecular weight polyethylene-elasticity modifier laminate composite and method of constructing the laminate composite, which laminate composite is designed to mount on the fifth wheel, trailer coupling plate or fifth wheel insert attached to the fifth wheel, to reduce friction between the trailer coupling plate and the fifth wheel or fifth wheel insert. In a preferred embodiment the laminate composite is constructed by mixing ultra-high molecular weight polyethylene resin with carbon fibers or other modulus of elasticity-modifying fibrous material, applying pressure to the mixture, producing a sheet of the composite of selected thickness, preparing the fifth wheel, trailer coupling plate or fifth wheel insert for bonding to the composite, preparing the sheet composite for bonding to the fifth wheel, trailer coupling plate or insert and bonding the laminate composite to the fifth wheel, trailer coupling plate or the fifth wheel insert by means of a suitable adhesive such as a urethane or an epoxy.